Hiroshi Niida

Magnetization and coercivity of Mn3−δGa alloys with a D022‐type structure

The D022‐type (Al3Ti‐type) phase in the Mn–Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis. The Curie temperature is about 765 K (for δ=0.67), near the decomposition temperature. We have prepared the D022‐type alloys by annealing the quenched ingots of the high‐temperature phase (γMn phase) at 400 or 300 °C for a long time. The preparation becomes much easier if the ingots are powdered by filing before the annealing. The single‐phase specimens of Mn3−δGa were obtained in the composition range 0.15≤δ≤1.06. The coercivity of some specimens was so large that we measured the magnetization curve in high magnetic fields up to 150 kOe. The room‐temperature values of saturation magnetization, remanent magnetization, and coercivity of the powder sample of the alloy with δ=0.67 are 50 emu/g, 25 emu/g, and 13.5 kOe, respectively. We have also studied the effect of magnetic annealing during the transition from the γMn phase to the D022‐type phase and the effect of the addition of F...

Magnetic Properties and Crystal Distortion of Hexagonal Mn3 Ga

Magnetization measurements and X-ray diffraction experiments have been made on e -Mn 3 Ga (71.4 at%Mn) having a triangular spin structure with a weak ferromagnetic component below 460 K. It has been found that the D0 19 -type hexagonal structure is slightly distorted to an orthorhombic structure below 170 K, and that the transition is accompanied by a steep increase of spontaneous magnetization. The crystal distortion may enhance the deviation from the ideal triangular spin configuration.

Structural and magnetic properties of Ni2In type (Mn1 − xNix)65Ga35 compounds

Abstract New intermetallic compounds (Mn 1 − x Ni x ) 65 Ga 35 of Ni 2 In type structure are found in the range of 0.15 ⩽ x ⩽ 0.45. In the higher x range, the magnetization—temperature curves show Curie—Weiss type behaviors, but those with x ⩽ 0.35 suggest another type ferromagnet. The magnetic ordering temperature T c decreases for x ⩽ 0.2 and then increases with increasing x . The curves of 0.25 ⩽ x ⩽ 0.3 show a hump and then slightly decrease with decreasing temperature. In the neutron diffraction experiment for x = 0.275, the (0 0 1) reflection appears for 165 K ⩽ T T C to 8.47 C with temperature.

Magnetic structure of γ-Mn(Ga) alloys with distorted cubic lattices

Abstract γ-Mn alloys containing Ga undergo a distortion from the face-centered-cubic structure to the face-centered-tetragonal structure with c/a 1, depending on composition. The face-centered-orthorhombic structure also exists in a composition range between the two tetragonal phases. The antiferromagnetic structures of these phases have been determined by neutron-diffraction experiments. The tetragonal and orthorhombic phases exhibit collinear and noncollinear moments, respectively. The results are consistent with the theoretical prediction by Jo et al.

Magnetic properties of hp13 type TiFe6Ge6 alloy

Abstract We have made magnetization measurements, Mossbauer spectroscopy and neutron diffraction on a hexagonal hp13 type TiFe6Ge6 alloy; the 1a and 6i sites are entirely occupied by Ti and Fe, respectively. The alloy exhibits a simple antiferromagnetism with the magnetic moment of about 1 μB/Fe atom at 12 K, the Neel temperature of 510 K and the paramagnetic Curie temperature of 70 K, and the internal field of 162 kOe at 295 K. This is in contrast with complicated magnetic properties of the isotypic alloys such as Fe5Mn2Ge6.

Antiferromagnetic to ferromagnetic transition of DO19 type (Mn1-xFex)3Sn1-δ

We have made X-ray and neutron diffraction experiments, and magnetization measurements for a pseudo-binary system (Mn 1- x Fe x ) 3 Sn 1-δ . In the region x x >0.4 show the typical ferromagnetism. The magnetic phase diagram of the system is proposed.

Crystal distortion and weak ferromagnetism of Mn3+δGa1−xGex alloys

The compound Mn3Ga (70–74 at.% Mn) has the hexagonal DO19‐type structure, and a triangular antiferromagnetic spin structure with a weak ferromagnetic component below the Neel temperature of about 470 K. Below 170 K the hexagonal structure is distorted to an orthorhombic one, accompanied by a steep increase in the ferromagnetic component. X‐ray‐diffraction experiments and magnetization measurements have been made for a pseudobinary system Mn3+δGa1−xGex. It was found that the DO19‐type structure is stable at 600 °C in the whole composition range 0≤x≤1.0 with appropriate values of δ. The Neel temperature of the triangular spin structure decreases with increasing x with a gentle slope. The crystal distortion temperature decreases more steeply and vanishes near x=0.6.

Magnetic phase transition in ϵ-(Mn1−xFex)3+δGe

Abstract A pseudo-binary system of ϵ-(Mn1−xFex)3+δGe (hexagonal DO19 type structure) has a collinear antiferromagnetic phase in a composition range near x = 0.2 at low temperatures. A field-induced transition from the collinear antiferromagnetic phase to the triangular antiferromagnetic phase (higher temperature phase) was observed in high fields of about 100 kOe.

Magnetic properties of (Mn1−xFex)3+δGe alloys

Abstract We have made X-ray, magnetization and electric resistivity measurements for (Mn 1−x Fe x ) 3+δ Ge with the D0 19 -type structure, and determined the x -dependence of the Neel temperature, the Curie temperature and a transition temperature from the triangular to the collinear magnetic structure for the alloys with δ=0.1 and 0 ⩽ x ⩽0.34. An abrupt change at the transition shows a remarkable thermal hysterisis.

Mössbauer Effect and X-ray Studies of the Phase Transitions in K 2 Fe(SO 4 ) 2 ·nH 2 O(n=2,4,6)

A detailed study of Mössbauer spectra for K 2 Fe(SO 4 ) 2 ·nH 2 O(n=2,4,6) has been performed. Isomer shift and quadrupole splitting of 57 Fe were measured as functions of temperature between 90 K and 370 K. Single crystals of dipotassium iron sulfate, K 2 Fe(SO 4 ) 2 ·nH 2 O were grown by slow evaporation of aqueous solutions of K 2 SO 4 and FeSO 4 in equimolar ratio. Since it was necessary to keep the solution above 360 K to obtain dihydrate crystals, K 2 Fe(SO 4 ) 2 ·2H 2 O was grown at 369 K. The crystal is known to undergo a phase transition which is associated with the water molecular orientation. The Mössbauer study was also performed on the crystals K 2 Fe(SO 4 ) 2 ·4H 2 O and K 2 Fe(SO 4 ) 2 ·6H 2 O for the search of the possible phase transitions similar to that of K 2 Fe(SO 4 ) 2 ·2H 2 O. The part of the X-ray structure analysis for these crystals is also given.